This invention relates to devices for inspecting the leads of integrated circuit or semiconductor devices. Known semiconductor device lead inspection systems are used to determine the position and orientation of semiconductor device leads after manufacture to find defects in the leads, such as bent leads, twist leads and the like. Prior art systems are mainly intended to provide a two dimensional view of the leads, which cannot be used to measure the lead standoff and coplanarity. In some cases, two or three imaging devices with various viewing angles are used to inspect device leads. In existing devices, the position of lead standoff may be measured from an optical reference point such as a track upon which the semiconductor device is positioned for purposes of inspection. In this event, the accuracy of positioning the device on the inspection station can affect the accuracy of the measurements of the lead positions.
It is an object of the present invention to provide images of a semiconductor device and its leads which provides geometrical information of the lead positions with respect to the edge of the semiconductor device body.
In accordance with the invention, there is provided an apparatus for providing first and second backlit images of a semiconductor device edge and leads extending therefrom. The images are representative of first and second viewing angles corresponding to first and second different optical axes as measured in a plane perpendicular to the device edge. The apparatus include at least one illuminator which provides diffuse backlit illumination of the device edge and leads in directions corresponding to first and second optical axis. A camera is arranged on an opposite side of the device edge from the illuminator along the first optical axis and oriented to form a direct image on the first optical axis. A reflector is arranged on the opposite side of the device edge and leads, along a second optical axis for deflecting a backlit image of the device edge and leads in a direction corresponding to the first optical axis toward the camera.
In one arrangement, the illuminator is an illuminated platform for holding the device. The camera is preferably arranged on a side of the device opposite the illuminated platform when the device is received on the platform. Where the device includes device edges and leads on two opposite sides of the device, two deflectors can be arranged for deflecting images corresponding to two of the second optical axes. In one embodiment the deflector comprises a prism, which may be a triangular right angle prism with a preferable edge angle of about 30 degrees. In this case, the deflecting can be internal reflection in the prism. The prism may have a surface which is paralleled to the first optical axis and a surface which is substantially perpendicular to the first optical axis. In another arrangement, the deflector may comprise a mirror. The mirror may form a plane which has an angle of 60 degrees from its normal to the first optical axis. In another arrangement there may be provided two illuminators, one for illuminating the device edge and leads along each of the optical axes. In this case, in one arrangement at least one of the illuminators may be arranged to move between an illuminating position and a withdrawn position which facilitates movement of a semiconductor device into an inspection position.
According to the invention, there is provided a method for providing first and second backlit images of a semiconductor device edge and leads extending therefrom. The images represent first and second viewing angles corresponding to first and second different optical axes as measured in a plane perpendicular to the device edge. The device edge and leads are illuminated with backlit light diffuse illumination radiating in directions corresponding to the first and second optical axes. A first backlit image of the device edge and leads is captured along a direction corresponding to the first optical axis. A second backlit image of the device edge and leads is deflected from a direction corresponding to the second optical axis to a direction corresponding to the first optical axis and the second backlit image is captured as deflected.
The illumination can be from one illuminator which is arranged to radiate in directions corresponding to the first and second optical axes toward the device edge and the leads. The first and second backlit images may be captured on a single image plane of a camera on a side of the device opposite the illuminator. In one arrangement, backlit images of device edges and leads on two opposite sides of a semiconductor device can be captured. A first backlit image of the two edges and leads is captured in a direction corresponding to a first optical axis and a second backlit image of each of the device edges and leads is deflected from directions corresponding to two of the second optical axes in directions corresponding to the first optical axis and the two deflected backlit images are captured. The deflecting can be accomplished using a prism or a mirror. The prism may provide internal reflection. The illumination may be provided from a first illuminator in a direction corresponding to the first optical axis and a second illuminator illuminating in directions corresponding to the second optical axis. The first illuminator may be moved between a first position in which it illuminates the device edge and a second withdrawn position which facilitates movement of a semiconductor device into an inspection station.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.